Patellar cutting guide

ABSTRACT

A patellar cutting guide is particularly useful in a method of minimally invasive knee arthroplasty in which an incision is made along the medial or lateral aspect of a patient&#39;s knee, exposing the knee joint. The patellar cutting guide includes a clamp configured to be located exterior to the knee over the anterior portion of the patella, a stop having at least one portion configured to extend through an incision to a location posterior to the patella, and a cutting guide defining a cutting slot. The clamp may have outwardly extending spikes for passage through the tissue overlying the patella and into engagement with the patella. The stop is movable relative to the clamp and/or cutting guide. In one embodiment, the cutting guide is offset laterally and posteriorly relative to the clamp so that the slot is aligned with a medially or laterally-formed incision in the knee.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/143,203 filed May 10, 2002, now U.S. Pat. No. 7,048,741.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for total kneearthroplasty.

BACKGROUND OF THE INVENTION

Total knee replacement (also known as total knee arthroplasty) surgeryis a common procedure that is performed on hundreds of thousands ofpeople each year. A number of circumstances may require replacement of aperson's knee. For example, excessive deterioration of knee cartilagemay necessitate knee replacement. This type of problem and otherinjuries to the knee may result from accidents, disease such asosteo-arthritis or rheumatoid arthritis, or other causes.

The knee joint or “knee” is formed by the bottom or distal end of thefemur (or “thigh bone”) which extends from the hip, the top or proximalend of the tibia (or “shin bone”) which extends to the ankle, and thepatella (or “knee cap”). The distal end of the femur and the proximalend of the tibia are covered by a smooth layer of cartilage which allowsthe femur and tibia to move smoothly against each other. The patellaalso has a smooth cartilage layer on its posterior surface to allowsmooth motion against the femur. However, certain conditions, mostcommonly arthritis, can cause permanent deterioration of the cartilage.When the cartilage wears away, the roughened surfaces of the femur,tibia and patella may rub against each other causing pain, stiffness andswelling.

One option for treating the permanent deterioration of the cartilage istotal knee replacement surgery. In a total knee replacement procedurethe end surfaces of the tibia and femur, and the posterior surface ofthe patella, are resurfaced. Generally, the surface that covers thefemoral section is made from smooth metal or ceramic, while the surfaceattached to the tibia is constructed of metal and a high-densitypolyethylene. The patella is also resurfaced with a high-densitypolyethylene.

The commonly known method for total knee replacement is illustrated inFIGS. 1A-1D. Illustrated in FIG. 1A is a front exterior view of a knee.The femur F, tibia T and patella P are illustrated in phantom view. Inaccordance with the existing total knee replacement procedure, an 8 to12 inch incision I is made over the anterior or front portion of theknee.

Next, as illustrated in FIG. 1B, the 8-12 inch anteriorly locatedincision is opened exposing the patella and retinacular tissue Rattached to both sides of the patella. The medial patellar retinaculumis incised, thereby allowing for the eversion of the patella P. Withflexion of the knee, the patella falls posteriorly out of the way sothat the interior of the kneejoint is completely exposed.

Next, the distal end of the femur F, the proximal end of the tibia T,and the posterior surface of the patella are machined for acceptance ofreplacement knee components. In general, this step comprises affixing acutting guide to the femur, tibia and patella, respectively, andutilizing a cutting apparatus to remove a thin layer of the arthriticsurface of the femur, tibia, and patella. Further, anterior dislocationof the tibia from the femur is required to prepare the tibia. As is wellknown, these steps are rather exacting and requires precision if properresection of the femur, tibia and patella is to be successful.

Knee replacement components are then connected to the tibia T and femurF as illustrated in FIG. 1C. Positioning occurs by instruments thatreference external landmarks or the intramedullary canal of the femur Fand tibia T. As illustrated, the components include a femoral componentFC which is connected to the femur F. The femoral component FC generallyhas an inner surface and outer surface. The inner surface abuts thedistal end of the femur F, and may include one or more elongate pegs ora box for impacting into the femur F. The femoral component is generallyattached to the end of the femur using a special acrylic bone cement, orby obtaining a tight “press fit” of the femoral component FC to thefemur F. The outer surface of the femoral component FC comprises one ofthe replacement knee surfaces.

The components also include a tibial component TC. This component has aninner surface and outer surface. The inner surface again mates to thetibia T, and as such may include a stem for impacting into the tibia T.As illustrated, the stem is somewhat long and driven into engagement byguiding the tibial component TC along the axis of the tibia T intoengagement with the proximal end of the tibia T. Because of theelongated tibial stem, the tibia must be dislocated anterior to thefemur for insertion of the tibial component. The tibial component TC isgenerally attached to the upper end of the tibia using bone cement orscrews. The outer surface of the tibial component TC attaches to ahigh-density polyethylene insert which comprises the other of thereplacement knee surfaces.

Though not illustrated, with the patella P in an everted position andexposed, the posterior of the patella P may be removed as well. Areplacement patella component may be affixed to the rear of the patellaP, again using bone cement.

FIG. 1D illustrates the assembled total knee replacement. Asillustrated, the femoral component FC rests upon the tibial componentTC. Relative motion is permitted between these two components, while atthe same time protecting the femur F and tibia T. The patellar componentPC glides along the femoral component with knee motion.

The existing method of total knee replacement illustrated in FIGS. 1A-1Dhas a number of disadvantages. One significant problem is that theprocedure is quite invasive and traumatizing. The procedure results in alarge incision and substantial stresses upon the body resulting in longperiods of recovery/rehabilitation, and extended periods ofhospitalization.

In particular, as can be seen, in order to resect the femur and tibia,and to provide sufficient access to the distal end of the femur andproximal end of the tibia, the patella must not only be moved, buteverted. The patella is connected to the quadriceps tendon and muscleproximally and to the patellar ligament distally, comprising theextensor mechanism. The extensor mechanism must be stretched in order topermit the patella to be displaced and everted so as to provide frontalaccess to the knee. This stretching results in substantial strain andtraumatization to the extensor mechanism and quadriceps muscle whichtakes a great deal of time to recover. In fact, in many instances apatient can not actively extend the knee for several days after theprocedure. Additionally, the patellar tendon, on occasion, is rupturedor pulled loose from the tibia due to excessive strain with eversion ofthe patella. Also, the knee is further traumatized by displacing ordislocating the tibia anterior to the femur for tibial preparation andtibial component insertion. This strains and traumatizes the ligamentsof the knee and may result in damage to the adjacent nerves and bloodvessels or lead to complication including blood clots, nerve palsy,arterial injury, excessive swelling, fracture or ligament avulsion.

In addition, the size of the incision is dependent on the need toprovide frontal access, including eversion of the patella, prepare thebony surface and guide the femoral, tibial and patellar components intoengagement with the femur, tibia and patella along axes thereof. Use ofa smaller frontal incision places excess tension on the skin, oftenresulting in skin necrosis or delayed healing. The large incisionresults in a long period of recovery and generally results in a visiblescar.

An improved method and apparatus for total knee replacement is desired.

SUMMARY OF THE INVENTION

The invention comprises a method of total or partial knee arthroplastywhich is minimally invasive, and one or more components for performingsuch a method.

In accordance with a method of the invention total knee arthroplasty isaccomplished in a minimally invasive manner through a small medial orlateral incision. In one embodiment, this incision is about 8-12 cmlong.

A method and apparatus is provided which permits total knee arthroplastywith minimal trauma to the patient. In accordance with the method, thepatella is not everted, nor is the tibia displaced or dislocated. Themethod of the invention is effectuated through the small medial orlateral incision without the need for access to the intramedullarycanals of the femur and tibia, and without the need for clearvisualization of common landmarks such as the epicondyles, posteriorcondylar surfaces, and tibial tubercle.

Apparatus, including cutting guides and implements, are preferablyconfigured to be located or attached along the side of the knee, and notthe front, and are further located extra-articular instead ofintra-articular. These devices and implements preferably permitpreparation of the knee through the small lateral or medial incision andplacement of trial and replacement knee components through the lateralor medial incision.

A patellar cutting guide is provided for resecting the patella withoutdissecting the overlying skin, subcutaneous tissues and bursa from thepatella, lessening the chance of skin necrosis from subcutaneousdissection, and lessening the chance of knee tenderness and inability ofthe patient to kneel after total knee replacement.

In accordance with one embodiment of the invention, the method includesthe step of creating an incision generally along the medial or lateralmid-line of the knee of a patient or somewhat anterior or posterior tothe medial or lateral midline. The incision is shorter in length thanthat used for the standard anterior approach, and preferably only about8-12 cm in length. The knee joint of the patient is accessed throughthis incision.

The distal end of the patient's femur at the knee joint is resected toaccept a femoral knee component. Likewise, the proximal end of the tibiaat the knee joint is resected to accept a tibial knee component. Thepatella is also resected to accept a patellar knee component. Thefemoral knee component is passed through the medial or lateral incisionand connected to the resected distal end of the femur. Likewise, thetibial knee component is passed through the incision and connected tothe resected proximal end of the tibia. If the patella is resected, thepatellar component is passed through the incision and connected to thepatella.

One embodiment of the invention comprises a femoral cutting guide whichcomprises a body having a slot therein for accepting a cuttingimplement. The femoral cutting guide is designed to be located externalto the side of the patient's knee, but guide the cutting implementthrough the medial or lateral incision during resecting of the femur.Unlike previous apparatus and techniques, the femoral cutting guide doesnot require eversion of the patella and extensor mechanism, nor requireaccess to the intramedullary canal or clear visualization of the commonlandmarks.

One embodiment of the invention comprises a tibial cutting guide whichcomprises a body which defines a cutting slot for a cutting implement.The tibial cutting guide is designed to be located external to the sideof the patient's knee, but guide the cutting implement through themedial or lateral incision during resecting of the tibia. Unlikeprevious apparatus and techniques, the tibial cutting apparatus does notrequire dislocation or displacement of the tibia from the femur, norrequire access to the intramedullary canal or clear visualization of thecommon landmarks.

One embodiment of the invention comprises a method of resecting thepatella without incising the overlying skin, sub-cutaneous tissues andbursa, and without everting the patella. In one embodiment, the methodcomprises engaging a first stop with the posterior of the patella and asecond stop with the anterior of the patella, locating a cutting guideexterior to the knee adjacent the medial or lateral incision, andpassing a cutting implement through the cutting guide and incision toresect the posterior of the patella.

One embodiment of the invention comprises a patellar cutting guide forpracticing the method, the cutting guide including a first portiondefining a slot for accepting a cutting implement and second and thirdstop portions. The first portion of the patellar cutting guide isdesigned to be located external to the patient's knee but guide thecutting implement through the medial or lateral incision duringresecting of the patella, while the second portion is designed to abutthe posterior of the patella for maintaining patella position duringresecting. A third portion of the patellar cutting guide is locatedexterior to the knee and includes spikes which penetrate the skin,engage the anterior of the patella and press it against the stop forsecure location during resecting.

In one embodiment, the femoral knee component is generally “C” shapedand includes a trough-shaped inner surface. The profile of the componentis minimized along the inner surface to permit the femoral kneecomponent to be inserted transversely through the medial or lateralincision and aligned with the resected femur, including withoutsubstantial dislocation of the femur relative to the tibia. To this end,in one embodiment, one or more engaging pegs extend outwardly from theinner surface for engaging one or more recesses in the femur, the lengthof the pegs minimized. In one embodiment, the femoral knee component isof the posterior cruciate ligament substituting design and includes acam for engagement by a post on a mating tibial knee component. In oneembodiment, the cam has a low profile, extending between a pair ofcondyle portions of the component and not extending upwardly into thetrough area of the component, again minimizing the profile of thecomponent.

In one embodiment, the tibial component is similarly constructed havinga low or small profile to insertion through the medial or lateralincision for impaction onto the proximal surface of the tibia. In thisregard, in one embodiment, the tibial component includes one or morepegs of reduced length and a short or absent central stem.

In one embodiment, the tibial component comprises a base and a matinginsert. In one embodiment, the base and insert are engageable in a“dove-tail” configuration, the base having a groove and the inserthaving a mating pin. In a preferred embodiment, the groove and pinextend in a lateral or transverse direction, permitting the insert to beinserted in alignment with the base through the medial or lateralincision.

One embodiment of the apparatus includes an impactor for impacting thetibial knee component and/or femoral knee component into engagement withthe tibia/femur. In one embodiment, the impactor is generally “U” shapedand includes a first arm for engaging the tibial or femoral kneecomponent through the incision, and a second arm which is then locatedexterior to the knee and upon which a force may be applied fortransmission to the tibial/femoral knee component.

In one embodiment of the invention, the method is performed with imageguidance assistance. An image is obtained of the patient's knee,including the femur, the tibia and patella. The image may be obtained byX-ray, fluoroscopy, CT scanning, or MRI. In one embodiment, no image ofthe knee is necessary and a pre-recorded 3-dimensional depiction of theknee joint is used, the dimensions based on measurements takenintra-operative.

One or more position sensors are attached to the tibia, femur and/orpatella, and/or one or more of the components, guides or other tools.Position data is generated by detectors placed in the operating roomusing a computerized image guidance system tracking the positions of theone or more sensors. In one embodiment, the position data is compared orcorrelated to the actual image data or the data obtained fromintra-operative measurements for visualization by a surgeon. Theposition and alignment data may be displayed on a display screen and beused, for example, in assuring proper preparation of the bony cuts ofthe femur, tibia and patella, positioning and alignment of the femoraland tibial knee components to the femur and tibia, including portionsthereof not visible by line of sight through the medial or lateralincision.

In another embodiment, the method is performed without such image guidedassistance. In one embodiment, an intra-medullary rod is passed througha small anterior incision of about 1 cm or less in length, and throughthe patellar tendon into the intra-medullary canal of the femur. Afemoral cutting guide is attached to the intra-medullary rod to allow itto align with the distal femur through the medial or lateral incision.Landmarks accessible through the medial or lateral incision areadditionally used to align the cutting guide with the distal femur. Thetibial cutting guide is aligned using a standard extra-medullaryalignment system but with the tibial guide in a medial or lateralposition to the proximal tibia to allow access to the tibia through themedial or lateral incision.

Further objects, features, and advantages of the present invention overthe prior art will become apparent from the detailed description of thedrawings which follows, when considered with the attached figures.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front or anterior view of a portion of a human patient'sleg illustrating the relative location and size of an incision used toaccess the knee for total knee replacement in accordance with the priorart;

FIG. 1B illustrates the knee of FIG. 1A with a patella and extensormechanism of the knee displaced and everted, exposing the femur andtibia of the leg in accordance with the method of total knee replacementof the prior art;

FIG. 1C is a side view of the knee wherein the femur and tibia have beenresected and replacement knee components are oriented for installationin accordance with the method of total knee replacement of the priorart;

FIG. 1D illustrates a replacement knee in accordance with the prior art,the replacement knee including a femoral component affixed to theresected femur, a tibial component affixed to the resected tibia, and apatellar component affixed to the resected patella;

FIG. 2 is a side view of a patient's leg illustrating the relativelocation of a medially or laterally located incision used to access theknee for total knee replacement in accordance with the presentinvention;

FIG. 3 illustrates the leg of FIG. 2 with the incision thereof opened toprovide access to the knee joint;

FIG. 4 illustrates a femoral cutting guide for use in resecting thedistal end of the femur for accepting a replacement femoral kneecomponent;

FIG. 5 illustrates a tibial cutting guide for use in resecting theproximal end of the tibia for accepting a replacement tibial kneecomponent;

FIG. 6 illustrates a patellar cutting guide for use in resecting thepatella for accepting a replacement patellar knee component;

FIG. 7 illustrates a replacement femoral knee component, replacementtibial knee component, and replacement patellar knee component of theinvention for connection to a resected femur, tibia and patella,respectively;

FIG. 8 illustrates an impactor for use in placing one or more of thereplacement knee components of the invention, including the tibialcomponent;

FIG. 9A is a front or anterior view of the knee of FIG. 7 illustrating afemoral and tibial knee component oriented for insertion through alateral incision in accordance with the invention;

FIG. 9B is a cross-sectional view of the knee illustrated in FIG. 9Ataken along line 9B-9B therein, and illustrating a patellar componentoriented for insertion through a lateral incision in accordance with theinvention;

FIG. 10A is a perspective view of a femoral component of a posteriorcruciate ligament retaining design;

FIG. 10B is a perspective view of a femoral component of a posteriorcruciate ligament substituting design;

FIG. 11A is a plan view of a tibial component for use with the femoralcomponent illustrated in FIG. 10A;

FIG. 11B is a plan view of a tibial component for use with the femoralcomponent illustrated in FIG. 10B;

FIG. 12A is a perspective view of the tibial component illustrated inFIG. 11A;

FIG. 12B is a perspective view of the tibial component illustrated inFIG. 11B;

FIG. 13A is a side view of a knee illustrating a femoral intra-medullaryrod passing through a small anterior incision and the patellar tendoninto the femoral canal, and further illustrating an arm connected to therod for supporting a femoral cutting guide in an aligned resectingposition;

FIG. 13B is a front view of the knee, rod, arm and cutting guideillustrated in FIG. 13A;

FIG. 14A is a side view of a knee illustrating a tibial cutting guideattached to an extra-medullary alignment guide in an aligned resectingposition; and

FIG. 14B is a front view of the knee, alignment guide and cutting guideillustrated in FIG. 14A.

DETAILED DESCRIPTION OF THE INVENTION

The invention is a method and apparatus for total knee arthroplasty. Inthe following description, numerous specific details are set forth inorder to provide a more thorough description of the present invention.It will be apparent, however, to one skilled in the art, that thepresent invention may be practiced without these specific details. Inother instances, well-known features have not been described in detailso as not to obscure the invention.

One embodiment of the invention is a method for total knee replacementwhich is minimally invasive. Referring to FIG. 2, in accordance with themethod, an incision I is made either generally medially or laterallyalong the mid-lateral line of the knee. By “generally” medially orlaterally, it is contemplated that the incision I may be somewhatanterior or posterior to the mid-lateral line. So located, the incisionI is generally centered over the tibio-femoral or “knee” joint. In apreferred embodiment, the incision I is about 8-12 centimeters long.

Several factors may be considered in determining whether the incision Ishould be located medially or laterally to the knee. The choice of exactincision location may depend upon any pre-operative deformity to becorrected. Generally, the ligaments on the concave side of the deformityare contracted requiring release. In this instance, the incision Ishould be made on the concave side of the deformity to allow forappropriate ligament balancing. The deep incision may divide ligamentstructures such as the medial collateral ligament or iliotibial bandalong the length of its fibers, but in general does not release theligaments transversely unless for ligament balancing. The incision maybe best made along the mid-lateral line on the medial or lateral side ofthe knee, or somewhat anterior or posterior to the mid-lateral linedepending on location of crucial ligamentous structures.

Referring to FIG. 3, access is provided to the knee joint through theincision I. One or more retractors or other devices may be used tospread or open the incision I. Notably, access is provided to the kneejoint without the need to evert the patella P. In a preferredembodiment, the patellar retinaculum is incised along the length of theincision in order to provide greater access to the knee joint, butagain, the patella P is not everted. Ligaments are released or elongatedto allow appropriate balancing and correction of deformity in accordancewith the standard practice of total knee replacement surgery.

A number of actions may be taken to provide access to and prepare theknee joint area for bony resection and affixation of the replacementknee components. In one embodiment, synovium may be excised, as may be aportion of the infrapatellar fat pad or body. The menisci and one orboth cruciate ligaments may be excised as is done in a standard totalknee replacement.

The proximal end of the tibia T and the distal end of the femur F arethen resected to accommodate the replacement knee components. Inaccordance with the method, access for resection is provided through themedial or laterally located incision I. Notably, unlike in the priorart, anterior displacement or dislocation of the tibia from the femur isnot necessary to adequately expose the proximal tibia.

Referring generally to FIG. 4, in one embodiment, a femoral cuttingguide 20 is located exterior to the patient's femur adjacent theincision I. A cutting apparatus is then used to resect the distal end ofthe femur F. Greater details regarding the femoral cutting guide 20 anda method of using an embodiment of the femoral cutting guide 20 of theinvention are detailed below.

Referring generally to FIG. 5, in one embodiment, a tibial cutting guide22 is located exterior to the patient's tibia adjacent the incision I. Acutting apparatus is then used to resect the proximal end of the tibiaT. Greater details regarding the tibial cutting guide 22 and method ofusing an embodiment of the tibial cutting guide 22 of the invention aredetailed below.

Referring generally to FIG. 6, in one embodiment, the patella P may beresected as well. A patellar cutting guide 24 may be used for thispurpose.

Referring to FIG. 7, replacement knee components are then implanted tore-surface the knee joint. As illustrated, the replacement kneecomponents include a femoral component 26 and a tibial component 28. Thereplacement knee components may also include a patellar component 30.Details regarding embodiments of these components are set forth below.

The components may be connected to the femur F, tibia T and patella P,respectively, in a variety of manners known in the art. In a preferredembodiment, the components include one or more short pegs, stems orother extensions for engagement with passages or recesses in the bone.Cement is the primary means for affixing the components to the bone,although screws and/or bone in-growth into a porous surface on the undersurfaces of the components may also be utilized.

Referring to FIG. 8, in one embodiment an impactor 32 may be used toaffix the tibial component 28 to the tibia T and the femoral component26 to the femur F. The impactor 32 is utilized to drive the femoralcomponent 26 onto the distal end of the femur F and the tibial component28 onto the proximal end of the tibia T. A clamp may be used to compressthe patellar component to the patella.

One or more embodiments of the invention comprise apparatus for totalknee arthroplasty, including total knee replacement components anddevices for preparing the bones and affixing the components to thebones. This apparatus and additional details of the method of theinvention will now be described.

As described above, in one step of a method of the invention, the distalend of the femur F is resected for fitting with the femoral kneecomponent 26. In one embodiment, the femoral cutting guide 20 is oneapparatus provided for this purpose. In general, the femoral cuttingguide 20 is designed to permit resection of the femur F through themedial or lateral incision I. Thus, unlike the anterior access of theprior art, in this embodiment the femoral cutting guide 20 must bedesigned for resecting the femur F where access is provided through onlya small medial or lateral incision I without the need for eversion ofthe patella.

To this end, in one embodiment, the femoral cutting guide 20 is arrangedto be located exterior to the femur of the patient on the medial orlateral side of the distal femur. As illustrated, the femoral cuttingguide 20 includes a body 40 having a slot or guideway 42 formed therein.In one embodiment, the body 40 is generally flat and plate-like.

The slot or guideway 42 is useful in guiding a cutting implement, suchas a reciprocating or oscillating saw or rotating milling device. Asdescribed below, such a cutting implement in one embodiment is extendedthrough the slot 42 generally perpendicular to the body 40.

As illustrated, in one embodiment, the slot or guideway 42 is generally“U”-shaped. A first portion 42 a of the slot 42 is arranged forresecting the anterior portion of the distal femur F and extendsgenerally parallel to the longitudinal axis of the femur. A secondportion 42 b of the slot 42 is arranged for resecting the distal end ofthe femur F and extends generally perpendicular to the longitudinal axisof the femur. A third portion 42 c of the slot 42 is arranged forresecting the posterior distal end of the femur F and extends generallyparallel to the longitudinal axis of the femur. Additional slots 42 d,42e may be arranged for angled resection of additional bone from thedistal femur.

It will be appreciated that in this arrangement, resection occursgenerally perpendicular to a plane extending in the anterior-posteriordirection through the knee joint, including the femur F. Using thefemoral cutting guide 20, the anterior portion of the distal femur F,the posterior portion of the distal femur F including the lateral andmedial condyles thereof, and the distal end of the femur F are allresected. The knee may be flexed or extended for each cut to moveligaments and neurovascular structure out the way to cause the leastchance of injury to these structures. Retractors or soft tissueprotectors may be inserted through the medial or lateral incision toprotect ligaments and neurovascular structures during cutting.

The femoral cutting guide 20 may be securely located in a variety ofmanners. In one embodiment, the femoral cutting guide 20 is connected tothe distal femur with pins, screws or the like. The femoral cuttingguide 20 is preferably securable in one or more fixed positions, or maybe adjustable once connected to the distal femur, to ensure properalignment for resecting the distal femur. As described below, a varietyofinethods and apparatus may be utilized to properly align the femoralcutting guide 20 before cutting.

The slot or guide 42 may have other shapes than illustrated, dependingupon the particular resected femur profile desired. In one or moreembodiments, the thickness of the body 40 may be varied to serve as acutting depth limiter for the cutting tool. Additionally, the body 40must be thick enough to stabilize the cutting instrument being passedthrough the slot 42 such that tilting of the cutting instrument andresultant over or under resecting does not occur.

The femoral cutting guide 20 may be constructed of a variety ofmaterials. In a preferred embodiment, the femoral cutting guide 20 isconstructed from an inert, durable and sterilizable material, such ascobalt chrome, stainless steel or ceramic.

As described above, in one step of a method of the invention, theproximal end of the tibia T is resected for fitting with the tibial kneecomponent 28. In one embodiment, the tibial cutting guide 22 is oneapparatus provided for this purpose. In general, the tibial cuttingguide 22 is designed to permit resecting of the tibia T through themedial or lateral incision I. Thus, unlike the anterior access of theprior art, in this embodiment the tibial cutting guide 22 must bedesigned for resecting of the tibia T where access is provided throughonly a small medial or lateral incision I. Anterior displacement ordislocation of the tibia from the femur is not required using thistechnique.

To this end, in one embodiment, the tibial cutting guide 22 is arrangedto be located exterior to the tibia of the patient on the medial orlateral side of the proximal tibia. As illustrated, the tibial cuttingguide 22 includes a body 50. In one embodiment, the body 50 isplate-like in form.

A slot or guideway 52 is formed in or defined by the body 50. The slotor guideway 52 is useful in accepting and guiding a cutting implement,such as a reciprocating or oscillating saw or other milling device. Aswith the femoral cutting guide 20, as detailed below, such a cuttingimplement is extended generally perpendicular to the body 50 duringcutting.

In the embodiment illustrated, the slot 52 has a generally planar area52 a for sectioning the proximal end of the tibia T in a horizontalplane generally 1-7 degrees posteriorly sloped to the longitudinal axisof the tibia T. To aid in locating the cutting implement and to avoidcutting beyond the anterior and posterior portions of the tibia T, firstand second cutting stops 52 b,c are located at either end of the slot52. Retractors or soft tissue protectors may be inserted through themedial or lateral incision I to protect ligaments and neurovascularstructures during cutting. The knee may be flexed or extended in orderto protect ligaments and neurovascular structures during different partsof the cut.

As with the femoral cutting guide 20, the tibial cutting guide 22 may besecurely positioned in a variety of manners. Secure fixation to thetibia may be achieved with pins or screws. One particular method ofsecuring the tibial cutting guide 22 is described in detail below inconjunction with FIGS. 14A and 14B. The tibial cutting guide 22 may alsobe constructed in a wide variety of manners other than that illustrated.For example, the shape of the slot 52 may vary depending upon thedesired resected tibial profile.

The tibial cutting guide 22 is preferably also constructed of a varietyof materials, and preferably an inert, durable and sterilizable materialsuch as cobalt chrome, stainless steel or ceramic.

As described above, in one step of a method of the invention, theposterior portion of the patella P may be resected for implanting withthe patellar knee component 30. In one embodiment, the patellar cuttingguide 24 is one apparatus provided for this purpose. In general, thepatellar cutting guide 24 is designed to permit resecting of the patellaP through the lateral or medial incision I. Thus, unlike the anterioraccess of the prior art, in this embodiment the patellar cutting guide24 must be designed for resecting the patella P where access is providedthrough only a small lateral or medial incision I. Eversion of thepatella is not required. Disection of the overlying skin, subcutaneoustissues and bursa is also not required.

To this end, in one embodiment, the patellar cutting guide 24 includes ameans for guiding a cutting implement, the means for guiding beingposition adjustable so that the depth of cut may be selected, and ameans for retaining or holding the patella during cutting. In onearrangement, the means for retaining includes a means for penetratingthe skin and subcutaneous tissues and engaging the anterior of thepatella, and a means extending through said medial or lateral incisionfor engaging the posterior of the patella.

In one embodiment, the patellar cutting guide 24 is arranged as a clampthat is affixed to the anterior and posterior surfaces of the patella.The patellar cutting guide 24 also defines a slot for guiding a cuttingimplement. In one embodiment, the patellar cutting guide 24 has twoparts. The first part comprises a body 60 which is arranged to belocated exterior to the knee. The body 60 defines a slot or guideway 62.The slot or guideway 62 is useful in guiding a cutting implement, suchas a reciprocating or oscillating saw or other milling device. In oneembodiment, the body 60 defines a generally elongate slot.

The body 60 also includes an arm or clamp 63. The arm or clamp 63 isarranged to extend along the exterior of the anterior of the kneepatella P when the portion of the body 60 defining the slot 62 isaligned with the medial or lateral incision I. It will thus beappreciated that the portion of the body 60 defining the slot 62 and thearm 63 do not lie in the same plane, horizontally or vertically.

Preferably, one or more spikes 65 extend from the arm 63. The spikes 65are preferably sharp, skin penetrating elements, designed to passthrough the skin and subcutaneous tissues and engage the patella P.

The patellar cutting guide 24 also includes a stop 61. The stop 61 isdesigned to extend into the medial or lateral incision I and engage theposterior of the patella P. In one embodiment, the stop 61 includes acupped or curved portion adapted to engage the posterior of the patellaP. In that at least a portion of the stop 61 is configured to be locatedat the posterior of the patella P while the portion of the body 60defining the slot 62 is located exterior to the knee, it will beappreciated that these portions do not lie in the same plane. However,in that the clamp 63 is configured to engage the anterior of the patellawhile a portion of the stop 61 engages the posterior of the patella, theclamp 63 and that portion of the stop may generally lie in the sameplane. As illustrated, the portion of the stop 61 and the portion of thearm or clamp 63 which are designed to be located adjacent the patella Pmay be curved or cupped to define a space there between in which thepatella P, tissue and the like may be located.

In a preferred embodiment, the stop 61 and the body 60 are hingedlyconnected, permitting them to be moved with respect to one another. Asillustrated, the stop 61 and the body 60 include lever arms 64 a,blocated on opposing sites of a hinge. These lever arms 64 a,b may beused to manipulate the relative position of the body 60 and stop 61.Preferably, the lever arms 64 a,b are used to compress the patella Pbetween the stop 61 and the arm 63, securely retaining it in a fixedposition while the patella is resected. In general, the patellar cuttingguide 24 is positioned so that the cutting implement, when located inthe slot 62, removes the posterior articular surface of the patella Pgenerally parallel to the anterior surface of the patella and at aspecified constant depth.

The patellar cutting guide 24 may also be constructed in a wide varietyof manners other than that illustrated. For example, the slot 62 mayhave a variety of shapes or sizes, as may the body 60 and arm 63. Forexample, the portion of the body 60 defining the slot 62 may beadjustable in position relative to the arm 63. In this manner, once thepatella P is fixed between the arm 63 and the stop 61, the location ofthe slot 62 may be adjusted so that the patella P is resected at theexact depth required or desired. For example, the slot 62 may be definedby a guide member which extends through a passage in the arm 63 andwhich can be fixed in a variety of positions with the set screw or thelike.

It will also be appreciated that the relative position of the stop 61and the body 60 may be adjustable by other than a hinged connection. Forexample, a rachet-slide or other moving connection may be used. Thepatellar cutting guide 24 may comprise individual elements which may ormay not be connectable (e.g. separate body defining a slot, arm orstop.) One or more spikes 65 may be used. Further, elements other thanspikes as illustrated may be used to engage the anterior of the patellaP.

In a preferred embodiment of the invention, means are provided fordetermining the relative positions of the guides, instruments, andcomponents during the procedure. In one embodiment, the means comprisesan image or computer assisted/guided system, which systems in and ofthemselves are well known in the prior art and which systems per se donot form the invention herein.

One embodiment of an image guided system is illustrated and will bedescribed herein. It will be understood that the system illustrated anddescribed is for reference only and a wide variety of other systems maybe utilized. These systems are often referred to under the term IGS for“image guided surgery.” In general, these systems generally employ atleast one sensor, at least two detectors, and a computer assistedguidance system. An image of a portion of a patient's body is displayed.Position information provided by the sensor and detectors is correlatedto the image, providing the viewer with a variety of information. Thesystem may be used to provide spacial position information, for example,of a surgeon's instruments relative to a portion of a patient's anatomy,or the relative positions of different portions of a patient's anatomy.

These systems may have a variety of configurations. As indicated ingreater detail below, the system may be arranged to accept a base imagein a variety of forms. For example, the system may be arranged to acceptand display an image of a portion of a patient's anatomy obtained byplain x-ray, fluoroscopy, magnetic resonance (MRI), computed topographic(CT) or other techniques. The sensors which are used to gain positioninformation which may be correlated to the image may be active orpassive. The position of passive sensors is generally obtained bydetectors external to the sensor, such as by using a beam of lightbounced off of the sensor. The position of an active sensor is generallyobtained by data transmitted or provided by the sensor itself to thedetectors. These sensors may be of a variety of configurations,depending on the particular system. Some sensors require a direct lineof sight between the sensor and the detectors, while others do not. Ofcourse, other systems now being developed or developed in the future mayalso be utilized.

In one embodiment, at least one position sensor is associated with eachbone and the cutting guide, instrument, resecting tools, or othercomponents. The position sensors are utilized to generate positioninformation for use with the cutting guide, instrument, resecting toolsor component placement.

Illustrated in FIG. 4 is one arrangement of an image guidance trackingsystem for reference in understanding a method of the invention. In thisembodiment, a position sensor 77 is connected to the femur F. Inaddition, a component sensor 74 is connected to the femoral cuttingguide 20.

In one embodiment of the invention, patient image data is obtained. Asindicated above, depending upon the system utilized, this image data maybe obtained using plain x-ray, fluoroscopy, magnetic resonance imaging(MRI), computed tomograph (CT) or other techniques. Image data isobtained regarding the patient's knee, including the femur, tibia andpatella. These images are loaded onto a computer workstation whichincludes a visible display device. In another embodiment, the knee isrepresented visually by a 3-dimensional depiction, such as a drawing,the dimensions of which are fed into the computer by direct measurementfrom the patient's anatomy.

The position sensors are utilized to determine the position of thepatient's actual bony anatomy, the cutting guides, instruments, cuttingtools, components or other tools. The actual position data is calibratedor compared against and illustrated on one of the patient images. Inthis manner, the physician is able to view the display and determine thetrue position of the components in relation to the patient's anatomy.This is particularly useful where the internal anatomy of the kneecannot be fully visualized or the visual alignment landmarks, such asthe tibial and femoral intramedullary canals, cannot be accessed.

In the embodiment illustrated, the position sensor 77 is utilized todetermine the position of the patient's femur F, which position is thencalibrated against the actual image data of the patient's femur F. Then,the position sensor 74 is utilized to determine the actual position ofthe femoral cutting guide 20. This information is calibrated against thefemur position and illustrated in relative spacial position on thedisplay. The surgeon may then determine, by viewing the display, thatthe femoral cutting guide 20 is correctly positioned. The cutting toolis then placed through the guide, and its position can be tracked, aswell, by using the display.

Referring to FIG. 5, similar sensors 76,78 may be used to determine theposition of the tibial cutting guide 22 relative to the tibia. Likewise,though not shown, similar sensors may be utilized to determine thelocation of the patellar cutting guide 24. Also, such sensors may beconnected to trial femoral, tibial and patellar knee components beforeinsertion of the final femoral knee component 26, tibial knee component28, and patellar knee component 30. Sensors may also be connected to theimpactor 32 or other instruments/components/tools.

These image assisting components are useful in providing the surgeonwith information which is otherwise limited due to the use of such asmall incision. In the prior art, the entire knee is widely exposed fromthe anterior approach and thus is entirely visible, and criticallandmarks such as the femoral and tibial intramedullary canals, thefemoral condyles, femoral epicondyles, and the tibial tubercle areeasily accessible. In the method of the invention, however, the size ofthe incision is minimized. In order to keep the incision as small aspossible, but still ensure proper resecting, alignment and componentplacement, the image guided system is preferably utilized. The imageassistance is useful, for example, in ensuring proper depth of resectionin the side opposite the incision (as a line of sight is not availablethrough the knee from the incision I to the opposite side).

As indicated, the method of the invention may also be performed withoutthe above-referenced image guidance assistance. In accordance with oneembodiment of the invention, various apparatus are provided for use in amethod of placing the components.

Referring to FIGS. 13A and 13B, in one embodiment of the invention, anintramedullary rod 100 is passed through a small anterior incision andthrough the patellar tendon into the intramedullary canal of the femurF. In one embodiment, the anterior incision is generally 1 cm long orless. The patellar tendon is incised in line with its fibers just distalto the patella P to permit passage of the rod 100.

The femoral cutting guide, such as the femoral cutting guide 20described above and illustrated in FIG. 4, is attached to theintramedullary rod 100 to align the femoral cutting guide with thedistal femur through the medial or lateral incision I. In oneembodiment, as illustrated, the femoral cutting guide is connected tothe intramedullary rod 100 using an arm 102. As illustrated, a first endor portion of the arm 102 is arranged to be selectively connected to therod 100. Preferably, the position of the arm 102 relative to the rod 100can be adjusted. As illustrated, the first end of the arm 102 includes asleeve 104 which accepts the rod 100, permitting the first end of thearm 102 to be moved along the rod 100 and be rotated about the rod 100.One or more set screws or the like (not shown) may be used to secure thearm 102 to the rod 100 in a fixed position.

The femoral cutting guide is connected to the second end of the arm 102.As illustrated, the arm 102 is configured so that when connected, thefemoral cutting guide is located along the side of the knee in alignmentwith the lateral or medial incision I. In the embodiment illustrated,the arm 102 is “L”-shaped having a first portion which extends outwardlyfrom the rod 100 and a second portion extending generally parallel tothe rod 100. The femoral cutting guide may be connected to the secondend of the arm 102 in a variety of manners, including by permanentconnection, mating threads and other means.

In accordance with the invention, the femoral cutting guide is placed inposition adjacent the distal femur along the medial or lateral incisionI. Utilizing landmarks which are accessible through the small medial orlateral incision I, such as the anterior shaft of the femur F, thecondyles or epicondyles, the femoral cutting guide is further alignedand then attached to the medial or lateral distal femur using pins,screws or the like. A cutting instrument is then passed through theguide to resect the distal femur F, as described above.

Referring to FIGS. 14A and 14B, an extra-medullary alignment guide 108is provided for aligning a tibial cutting guide, such as the tibialcutting guide 22 described above and illustrated in FIG. 5. Asillustrated, the extra-medullary alignment guide 108 comprises anelongate member having a first end and a second end. At each end, aclamp 110 is provided. As illustrated, each clamp 110 comprises agenerally “C” or “V” shaped member for extension about the exterior ofthe leg of a patient. These clamps 110 provide support for the elongatecentral portion of the guide 108. Of course, the alignment guide 108 mayhave a variety of other configurations.

The tibial cutting guide is connected to the extra-medullary alignmentguide 108, such as with an arm 12. Once again, means of connection maybe provided permitting the position of the arm 112, and thus a connectedcutting guide, to be moved relative to the alignment guide 108 foralignment purposes. The tibial cutting guide may also be connected tothe arm 112 in a variety of manners, including by means permitting thetibial cutting guide to be disconnected from the arm 112.

Once the arm 112 and tibial cutting guide are connected to one anotherand the extra-medullary alignment guide 108, the tibial cutting guide isaligned along the medial or lateral proximal tibia with the coronal andsagittal planes. The tibial cutting guide can then be securely connectedto the tibia through the medial or lateral incision, such as with pins,screws or the like as described above. A cutting instrument may then beused to resect the proximal tibia as guided by the tibial cutting guide.

In accordance with this apparatus and the above-described methods, thefemoral and tibial cutting guides are aligned using available anatomiclandmarks utilizing instrumentation that is specifically adapted toallow access of the femoral intra-medullary canal and other anatomicallandmarks without use of a large incision, eversion of the patella, oranterior displacement of the tibia from the femur. Cutting guides andalignment instruments are modified to be attached to the distal femurand proximal tibia through a small medial or lateral incision, with theaddition of a much smaller accessory anterior incision for placement ofthe femoral intra-medullary rod. Additional instruments for positioningof the cutting guides are modified for use through the small medial orlateral incision. In general, these instruments are small, compact, anddesigned to facilitate referencing the anterior, distal, posterior,medial, and lateral femur, and the upper surface of the tibia to allowappropriate positioning and fixation of the cutting guides to the medialor lateral femur and tibia through a very small incision.

In one or more embodiments of the invention, a specially configuredfemoral component 26, tibial component 28 and patellar component 30 areprovided. In general, these components are specially designed to bothact as total knee replacement components, and are also adapted to bepositioned through the miniature medial or lateral incision I.

Referring to FIG. 7, in one embodiment, the femoral component 26comprises a body 80 having an inner surface 82 and outer surface 84. Asdescribed below, when the femoral component 26 is connected to the femurF, the inner surface 82 is directed against the femur F. The outersurface 84 is located for contact against a mating surface of the tibialcomponent 28 and patellar component 30. As illustrated, the femoralcomponent 26 is generally “C”-shaped, with the inner surface 82 havingthe shape of a trough.

One or more fixation pegs 86 extend from the inner surface 82. The pegs86 are preferably very short in dimension. In one embodiment, the pegs86 are no longer than about 5-10 mm long. In another embodiment of theinvention, the femoral component 26 does not include the pegs. Ingeneral, it is desired that the pegs 86 be short or non-existent. Thepegs 86 may have a variety of shapes and configurations, but arepreferably generally circular in cross-sectional shape. This arrangementpermits the surgeon to align the “trough” shaped inner surface 82 withthe femur F from the medial or lateral side, and extend it transverselythrough the incision I into engagement with the femur F, as illustratedin FIG. 9A. Minimizing the length of the pegs 86 minimizes the distancethat the femoral component 26 must be offset downwardly along the axisof the femur F from the distal end of the femur F in order to locate thefemoral component 26 at the distal end of the femur F. Once positionedin the correct medial-lateral position, the femoral component is driveninto the distal end of the femur F utilizing the impactor 32.

The femoral component may be of a posterior cruciate ligament retainingdesign or of a posterior cruciate substituting design, as illustrated inFIGS. 10A and 10B, and as is well known in the prior art. FIG. 10Aillustrates a femoral component 26A without pegs of a posterior cruciateligament retaining design. This femoral component 26A is generally“C”-shaped, and has a generally upwardly extending anterior portion 110Aand a generally upstanding posterior portion 112A, with a trough 114Alocated there between. The femoral component 26A has an inner surface116A and an outer surface 118A. The inner surface 116A is for mating toa resected femur. The outer surface 118A is for abutting a tibialcomponent. As illustrated, the posterior portion 112A comprises a pairof separated medial and lateral condyle portions 120A, 122A.

Advantageously, the femoral component 26A has a low profile in thelateral or transverse (i.e. in a direction aligned with the trough)direction. In other words, the maximum distance between the inner andouter surfaces 116A, 118A, especially in the area of the trough, isrelatively small. In this manner, the femoral component 26A may bealigned laterally with the femur (as illustrated in FIG. 7), andinserted through the medial or lateral incision I and placed onto thefemur F with little displacement of the femur relative to the tibia.

FIG. 10B illustrates a femoral component 26B of a posterior cruciatesubstituting design. This embodiment component has a cam 27B between theposterior aspect of the medial and lateral condyle portions to contact apost 35B on a complimentary tibial insert (see FIG. 11B). Preferably,the cam 27B has a low profile and does not extend upwardly beyond theupper or inner surface of the condyle portions, again contributing to alow profile and minimizing interference during lateral insertion andalignment of the component 26B with the femur.

In this design, the cam 27B cooperates with the post 35B of the tibialcomponent 28B to prevent posterior sublutation of the tibia on the femurwith knee flexion. Notably, this style of posteriorly stabilized femoralcomponent 26B has a low profile, with no inset box or walls extendingupwardly from the inner surface, unlike that found with otherposteriorly stabilized components.

Referring again to FIG. 7, in one embodiment, the tibial component 28also comprises a body 90. As is known, the tibial component 28 has aninsert 92, such as made of plastic which forms the mating surface forthe outer surface of the femoral component 26.

In one embodiment, one or more pegs 94,96 extend from the under side ofthe tibial component 28 opposite the insert 92. The pegs 94,96 arepreferably of a very short dimension, preferably being no more thanabout 5-10 mm long. The pegs 94,96 may be of a variety of shapes andconfigurations. In one embodiment, the pegs 94,96 have a generallycircular cross-sectional shape. Once again, the pegs 94,96 of the tibialcomponent 28 are minimized for the same reasons that the pegs 86 of thefemoral component 26 are also minimized. This arrangement allows thetibial component to be inserted transversely over the proximal tibiathrough the medial or lateral incision and then onto the surface of thetibia using the impactor 32, as illustrated in FIG. 9A.

In one embodiment, the tibial component 28 comprises a base for affixingto the tibia, and an insert which is affixed to the base and comprisesthe surface which engages the femoral component. In one embodiment, thebase is constructed of cobalt chrome, titanium or ceramic and the insertof high density polyethylene.

The tibial component may be of a symmetric or asymmetric design withrespect to the medial and lateral aspects. The polyethylene insert isdesigned to mate tightly with the tibial component using a dovetailmechanism. The polyethylene insert is designed for insertion into thebase from the medial or lateral side. A locking mechanism such as a stepon the medial and lateral sides of the base allow secure locking of thepolyethylene insert into the tibial component when fully inserted.

FIGS. 11A and 12A illustrate in detail one embodiment of a tibialcomponent 28A including a base 31A and insert 33A. This embodimenttibial component 28A is partially suited for use with the femoralcomponent 26A illustrated in FIG. 10A. As illustrated, the base 31A andinsert 33A have a mating pin and groove or “dovetail” configuration. Thebase 31A and insert 33A both have anterior 125A and posterior 127Aportions, and opposing sides located between the anterior and posteriorportions 125A,127A. A slight depression is formed in a top surface ofthe insert 33A between the anterior and posterior portions 125A, 127A,formatting with the outer surface of a femoral component.

A groove 126A is formed in the top of the base 31A and extends in alateral (i.e. side to side) direction. Likewise, a mating pin 128A isdefined by the lower surface of the insert 33A, the pin 128A extendingin a lateral direction, permitting alignment and insertion of the insert33A through the medial or lateral incision I into the groove 126A of thebase 31A.

The pin 128A and groove 126A may be formed in a variety of fashions. Asillustrated, the pin 128A comprises a downwardly extending area of thebottom of the insert 33A. In the embodiment illustrated, the groove 126Adefines a pair of overhanging ledges 130A for mating with a pair ofextensions 132A of the pin 128A. The ledges 130A and extensions 132Aengage, permitting lateral movement of the insert 33A relative to thebase 31A for insertion, but preventing front to back or upward movementof the insert 33A relative to the base 31A. Other mating configurationsmay be utilized, but preferably, such configurations permit the lateralinsertion and alignment of the components as described.

FIGS. 11B and 12B illustrate an embodiment of a tibial component 28Bwhich includes a post 35B in the center of the polyethylene insert whichis arranged to mate with the femoral cam of a posterior cruciateligament substituting femoral component as illustrated in FIG. 10B.

The patellar component 30 may have a variety of configurations includingthose already known. Once positioned against the cut surface of thepatella, it is held with a compression clamp while the bone cementhardens or to press fit against the patella P.

One aspect of the invention is one or more tools or devices for use inplacing the components. Illustrated in FIG. 8 is one embodiment of animpactor 32 for use in placing the femoral component 26 or tibialcomponent 28. The impactor 32 includes a contact arm 101 and a drivingarm 105 connected by a support 103. The general shape of the impactor 32is generally “U” or “C”-shaped, such that the contact arm 101 may beplaced through the medial or lateral incision I and against the femoralor tibial component 26,28, while the driving arm 105 is located outsideof the knee. The driving arm 105 may, as illustrated, include anupwardly extending post or driver designed to transmit the force ofhammer blows to the contact arm 101.

In one embodiment, the impactor 32 is constructed of a rigid, durableand sterilizable material such as stainless steel. The exact dimensionsof the impactor 32 may vary. Preferably, however, the length of thecontact arm 101 is sufficient to extend from the support 103 whenlocated outside of the incision I adjacent the patient's leg, to aposition over the femoral component 26 placed in position at the femur For the tibial component 28 placed in position at the tibia T. Inaddition, the driving arm 105 is also sufficiently long to extend fromthe opposing end of the support 103 to a point generally above thedistal end of the femur F or proximal end of the tibia T adjacent to thepatient's leg.

In use, the surgeon locates the femoral component 26 or tibial component28. The surgeon then locates the driving arm 105 of the impactor 32against the femoral component 26 or tibial component 28 (or if thetibial component 28 has a base and insert against the base) by extendingthe contact arm 101 through the incision I. The surgeon may then impactupon the driving arm 105, which force is transmitted through theimpactor 32 to the tibial component 28. This force is useful, forexample, in pressing the pegs 86 of the femoral component 26 or the pegs94,96 of the tibial component 28 into bores or recesses formed in thefemur F for the tibia T.

Other specialized instruments designed for use through the short medialor lateral incision I may include hooks or “back-biting” curettes toremove bone spurs from the femur and tibia, soft tissue protectors whichcan be inserted to protect the anterior or posterior soft tissue, andhooked or curved curettes or spatulas to remove excess cement fromaround the components. Curved osteotomes may be utilized for removal offemoral or tibial bonus spurs. A sizing caliper or depth gauge may benecessary to measure the dimension of any of the three bones for correctsizing of the implant components.

In one or more embodiments, trial components may be used during themethod. A trial femoral component, tibial component and/or patellarcomponent may be used before the actual components are permanentlyplaced in order to ensure proper resection of the femur, tibia andpatella and ligament balancing. These trial components may be shapedsimilar to the actual components, but may be made of lightweight metalor plastic. The trial components need not have the same exactingtolerances and the same durability as the actual components.

In one embodiment, one or more sensors may be connected to the trialcomponents. Position information provided by the sensors may be used inthe trial placement process to aid in alignment of the actual componentsand assessment of the ligament tightness.

The method and apparatus of the invention have numerous benefits. Inaccordance with the invention, a method is provided for total kneearthroplasty in a minimally invasive manner. Access to the knee joint isprovided through a short medially or laterally located incision. Due tothe medial or lateral location, access is provided to the knee jointthrough an incision which is much smaller than the size of incisionwhich would be necessary to access the knee joint from the anterior.

The small medial or lateral incision permits full access to the kneejoint, including the distal end of the femur and the proximal end of thetibia. Access is provided without the need to evert the patella. Accessthrough the medial or lateral incision is the primary reason for notneeding to evert the patella, and at the same time, because the patellaneed not be everted, the size of the incision which is necessary toprovide access is substantially reduced. The medial or lateral incisionalso does not require anterior displacement or dislocation of the tibiafrom the femur for preparation of the tibia or insertion of the tibialcomponent.

Access to the knee joint via the medial or lateral incision is alsoadvantageous when considering the resection of the femur, tibia andpatella. As illustrated in FIGS. 7 and 9, all of the various planes ofresection are accessible from the medial or lateral side of the knee,including the anterior portion of the distal femur F, the distal end ofthe femur F, the posterior portion of the distal femur F, the proximalend of the tibia T and the patella P.

The greatest advantage realized by the invention is that partial ortotal knee arthroplasty can be realized with much less trauma to thepatient. The trauma to the patient is reduced because the size of theincision is greatly reduced. In addition, the patellar ligament andquadriceps tendon and muscle are not over-extended, stretched, or tornbecause the patella is not everted. Also, the tibia is not dislocatedwith resultant potential injury to the knee ligaments and othersurrounding structures.

An improved femoral component 26 and tibial component 28 are providedwhich have aspects of reduced dimensions that allow for a small medialor lateral incision. As indicated, each component 26,28 is designed withshort fixation pegs to allow insertion without excessive displacement ordislocation of the joint. The posterior stabilized femoral component hasa low profile on the inner surface to facilitate insertion through themedial or lateral incision without excessive displacement of the tibiafrom the femur or need for a longer incision. Compared to prior artfemoral components 26 of the posterior cruciate ligament substitutingdesign, the femoral component 26 has no box or protective side-wallswhich extend upwardly from the inner surface to surround a mating postof the tibial component. Thus, the femoral component 26 of the inventionhas a substantially reduced lateral profile relative to prior artcomponents.

The tibial component comprising a base and polyethylene insert aredesigned such that the insert can be slid into place and locked securelyto the base from the medial or lateral side without displacement ordislocation of the joint. These design characteristics allow insertionthrough a minimized medial or lateral incision.

Additional components are provided for use in preparing the knee jointfor accepting the replacement components and placing those components.These components are specially designed to be used in conjunction with amedially or laterally located incision I.

Advantageously, the method of the invention is effectuated through thesmall medial or lateral incision without the need for access to theintramedullary canals of the femur and tibia, and without the need forclear visualization of common landmarks such as the epicondyles,posterior condylar surfaces, and tibial tubercle.

The cutting guides and implements are arranged to be located or attachedalong the side of the knee, and not the front, and are further locatedextra-articular instead of intra-articular. These devices and implementspermit preparation of the knee through the small lateral or medialincision and placement of trial and replacement knee components throughthe lateral or medial incision.

In one configuration, a patellar cutting guide is provided for resectingthe patella without dissecting the overlying skin, subcutaneous tissuesand bursa from the patella, lessening the chance of skin necrosis fromsubcutaneous dissection, and lessening the chance of knee tenderness andinability of the patient to kneel after total knee replacement.

It will be understood that the above described arrangements of apparatusand the method therefrom are merely illustrative of applications of theprinciples of this invention and many other embodiments andmodifications may be made without departing from the spirit and scope ofthe invention as defined in the claims.

1. A patellar cutting guide for use in resecting a posterior portion of a patella through an incision generally located along the medial or lateral mid-line of a knee, comprising: a stop for location posterior to a posterior portion of said patella having a surface configured to abut a posterior portion of said patella, said surface further configured to extend from a distal portion of said posterior portion of said patella to a proximal portion of said posterior portion of said patella when said stop abuts said patella; a cutting guide oriented generally perpendicular to said stop, said cutting guide having a generally longitudinal, slot therein for accepting a cutting implement for resecting a posterior portion of said patella; a clamp having at least one spike extending therefrom in a direction of said stop, said spike adapted to penetrate the skin and engage an anterior portion of said patella such that said clamp and said stop exert opposite forces posteriorly and anteriorly, respectively; and means for moving said clamp relative to said stop, whereby said clamp and stop may be moved into relative positions in which they secure said patella in a fixed position while said cutting implement is utilized to resect said patella.
 2. The patellar cutting guide in accordance with claim 1 wherein said means for moving comprises a pivoting connection of said clamp and stop.
 3. The patellar cutting guide in accordance with claim 2 wherein said pivoting connection comprises at least one pin, and including a first lever arm extending from a portion of said clamp opposite said pin and a second lever arm extending from a portion of said stop opposite said pin.
 4. The patellar cutting guide in accordance with claim 1 wherein said cutting guide is connected to said clamp.
 5. A patellar cutting guide for use in resecting a posterior portion of a patella of a knee of a patient, comprising: a stop, said stop having a proximal portion and a distal portion, said distal portion configured to be extended through an incision in said knee; and a body configured to be located exterior to a knee of a patient, said body defining an elongate slot through which a cutting implement may be passed for resecting a posterior portion of said patella, said body further defining a clamp configured to engage said knee patella at anterior of said patella, said stop and said body movably connected to one another whereby said stop and body may be moved relative to one another and oriented such that when said stop and said body are moved relative to one another, said stop and said body clamp said patella by exerting opposing forces in the posterior-anterior direction of the patella.
 6. The patellar cutting guide in accordance with claim 5 wherein said clamp defines a plurality of outwardly extending spikes.
 7. The patellar cutting guide in accordance with claim 6 wherein said spikes extend towards said stop.
 8. The patellar cutting guide in accordance with claim 5 wherein in said body and said stop are pivotally connected by at least one pin.
 9. The patellar cutting guide in accordance with claim 5 wherein said clamp of said body and said stop lie generally in a first plane on at opposing sides of said patella when said cutting guide is in position and said slot is located in a guideway which is located in a second plane which is offset from said first plane.
 10. The patellar cutting guide in accordance with claim 5 wherein said slot is defined by a guideway portion of said body.
 11. The patellar cutting guide in accordance with claim 5 wherein said clamp and said stop extend outwardly in opposing directions from one another from a point at which said body and stop are connected to one another for relative movement.
 12. The patellar cutting guide in accordance with claim 5 wherein said proximal portion of said stop comprises a first lever arm and wherein said body is connected to a second lever arm.
 13. A patellar cutting guide for use in resecting the posterior of a patella through a lateral incision in a knee of a patient, the lateral incision thereby defining the boundary between an anterior portion of the knee and an exterior portion of the knee comprising: a clamp configured to engage said exterior portion of said knee overlying anterior portion of said patella; a stop having a proximal portion and a distal portion, said proximal portion configured to pass through said lateral incision and engage a posterior portion of said patella while said proximal portion remains exterior to said knee; and a cutting guide, said cutting guide offset laterally and posteriorly from said clamp, said cutting guide defining a cutting slot, said slot aligned with along said lateral incision when said clamp and stop engage said patella.
 14. The patellar cutting guide in accordance with claim 13 including one or more spikes extending from said clamp for passage through tissue overlying said anterior portion of said patella and pass into engagement with said patella.
 15. The patellar cutting guide in accordance with claim 13 wherein said clamp and cutting guide are defined by a body.
 16. The patellar cutting guide in accordance with claim 15 wherein said body defines a lever arm and said lever arm and said distal portion of said stop are movable connected to one another, permitting the relative position of said stop to be changed relative to said body. 